Method of reinforcing a paved surface

ABSTRACT

To form a paved surface, a laminate is used which has on the bottom a geotextile fabric with the mesh structure on the top. The fabric is adhered to the road base by spraying or spreading a bituminous liquid onto the base and laying on the laminate and applying further adhesive to the top of the laminate; asphalt is then placed and rolled. The laminate is formed of a square or rectangular mesh structure which has oriented stands connected at junctions which are thicker than the strands and have low-orientated or unorientated nodules. On one side the surface of the nodules are melted and the fabric is pressed into the nodules so that the plastics material of the nodules envelopes some of the fibres or filaments of the fabric to form a mechanical bond. In this way, the oriented strands stand proud of the fabric, to enable the asphalt aggregate to penetrate into the meshes and interlock with the strands.

This is a continuation of application Ser. No. 07/634,807, filed Dec.31, 1990, now abandoned, which is a continuation of application Ser. No.07/432,669, filed Nov. 07, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a method of reinforcing a paved surface, andalso to a reinforcement for use in the method.

The invention is applicable to paved surfaces in general, but theinvention is particularly useful when reinforcing asphalt. "Asphalt" isused herein in the general sense to refer to an aggregate having ahydrocarbon-type binder, which may be for instance natural asphalt orbitumen; the asphalt is normally laid hot and sets on cooling, thoughcold-mix asphalts can be used. The asphalt can be used on for instance aroad or runway, normal practice being to lay an asphalt base course andto place an asphalt wearing course over the base or binder course. Theground is the surface to be covered with a paving layer, and can be anysuitable surface, and can eventually be within a multi-layerconstruction, e.g. within the thickness of a full depth asphalt pavementor road. The ground can be e.g. the surface of a lower layer of asphaltor concrete to be covered with an upper layer of asphalt, or the base orbinder course, or the lower part of an old wearing course whenrefurbishing, or a concrete or lean-mix concrete base or sub-base. Thusthe invention can be applied when making a new construction or whenrefurbishing, for instance, after part or whole removal of the oldwearing course, or even directly onto an old wearing course.

In recent years, mesh structures (which are also termed grids) have beenincorporated in order to improve the paved surface. The mesh structurecan control rutting and reflective cracking (cracking which is initiatedin or below the base course). The mesh structure itself is laid onto theground and is tensioned, the tension being maintained throughout thelaying process. Modern practice is to spray the mesh structure and theground with a bituminous emulsion or solvent-based bitumen known as"cut-back", and a layer of small stone chippings is then spread over thesurface, becoming adhered to the bitumen. A conventional pavingoperation can then be carried out to apply a layer of hot asphalt ontothe layer of chippings without the tracks or wheels of the asphaltlaying machine (called a paviour) coming into contact with the grid. Thelayer of hot asphalt becomes integrated with the layer of chippings andbitumen, the whole composite being bonded to the road surface throughthe bitumen. Vertical loads on the new road surface are resolved intohorizontal forces, which are then restrained by the grid structure intowhich the chippings and aggregate from the asphalt layer interlock.

Whilst this procedure is effective, it is complex and relativelyexpensive because of the number of individual operations necessary. Thecoating of the ground and mesh structure with bitumen and then spreadinga chip coat, is expensive and time consuming.

The mesh structure itself is preferably formed of plastics material,high-strength molecularly oriented polymer structures being used, forinstance, a biaxially-oriented mesh in accordance with U.S. Pat. No.4,374,798. However, other materials such as glass fibre grids, woven orknitted polyester meshes or metal grids may be used.

A commercially-acceptable method is desirable for positioning the meshstructure in the asphalt. In one experimental procedure, the meshstructure was laid on top of the base or binder course and the wearingcourse placed on top of the mesh structure using a conventional machine;the mesh structure was a biaxially-orientated mesh structure inaccordance with U.S. Pat. No. 4,374,798. It was found that if the meshstructure was merely laid on the surface of the base or binder course,the tractive forces and weight of the asphalt laying machine caused themesh structure to stretch and buckle as the wearing course was laid,resulting in the mesh structure being imprecisely positioned and causingsubsequent rucking of the mesh structure and splitting of the asphalt.The mesh structure moves forward in front of the wheels or track of themachine, forming a type of bow wave. This makes it impossible todetermine the position of the mesh structure within the wearing course.

THE INVENTION

According to one aspect of the invention, a mesh structure/fabriclaminate is adhered to the ground with the fabric lowermost, andaggregate is placed on the laminate to form a reinforced paved surface.

According to a second aspect of the invention, a mesh structure/fabriclaminate is produced by providing a plastics material mesh structurecomprising oriented strands connected to each other at junctionscontaining parts which are substantially thicker than the strands, standproud of the strands, and contain plastics material which isunorientated or of low orientation, melting the surfaces of said thickerparts, and pressing a fabric onto the mesh structure so that theplastics material of said thicker parts envelopes some of the fibres offilaments of the fabric and thereby bonds said thicker parts to thefabric without bonding the strands of the mesh structure to the fabric.

The reinforcing method of the invention makes it unnecessary to tensionthe mesh structure as it is being laid. Nonetheless, as the laminate isproperly retained by adhesion to the ground, the mesh structure does notstretch and does not form bow waves as the asphalt laying machineadvances. The fabric provides a good medium for adhering or bonding tothe ground, but does not prevent interlock between pieces of aggregateand the mesh structure, which is important for effective reinforcementby the mesh structure. No significant plane of weakness is formed. If,as is preferred, the mesh structure comprises strands and parts whichare thicker than the strands, which parts are secured to the fabric toform the laminate, the strands can stand slightly proud of the fabric,which improves interlock.

Using the invention, the normal paving operation can be carried outwithout the necessity for the application of the chippings to the meshstructure, though some time may be required to allow the adhesive tocure.

The laminate may be adhered to the ground by using a liquid which issprayed or spread on the ground before laying laminate, and a secondapplication of liquid may be made to the top of the laminate afterlaying the laminate on the ground. The fabric not only absorbs theliquid, but allows the liquid to pass through the fabric so forming abond as the liquid cures or sets, and adhering the fabric to the ground.The fabric can be secured firmly to the adhesive by brushing it onto theground with push brooms or automatic equipment having the same action.Some time must be allowed for curing or setting before proper adhesionis achieved.

The fabric can be of any suitable type, but will have a fibrous orfilamentary structure suitable for mechanical interlock with the curedor set adhesive. It should be sufficiently coherent to provide a goodbond between the mesh structure and the ground, though the presence ofthe adhesive in the intesticies of the fabric can achieve this. Thepreferred fabrics are needled continuous filaments or staple fibres orspun bonded fabrics, but woven or knitted fabrics could be used. Thefabric will normally be formed of a plastics material such as polyester.Suitable geotextile fabrics are known.

Any suitable adhesive can be used, and adhesion may be due for instanceto a chemical change, solidification on cooling or solidification as asolvent evaporates. The adhesive could be an aqueous based bituminousemulsion or a solvent based bitumen known as "cut-back" or "purebitumen". The rate of application of the adhesive will depend on theweight of fabric being used and also the standard of finish on theground on which the fabric is laid, but sufficient needs to be appliedto ensure an adequate bond to the ground.

The unit weight of the fabric could be from 80 gms/m² to 250 gms/m², butpreferably about 130 gms/m².

The mesh structure can be made from any suitable material by anysuitable method, but is preferably made from polypropylene or polyester,and is preferably made by the method described in U.S. Pat. No.4,374,798. The mesh pitch could be from 30 mm to 100 mm, but preferablyis from 40 mm to 75 mm. The weight of the grid structure could be from150 gms/m² to 400 gms/m² but is preferably about 240 gms/m².

The size of aggregate included in the surface layer will depend on thepurpose to which the surface is to be put, but will range from 3 mm to40 mm as single sizes or in a specified grading range.

The particular laminate of the invention is especially useful in thereinforcing method of the invention--as explained above, the strands canstand slightly proud of the fabric. The plastics material of the thickerparts envelopes some of the fibres or filaments of the fabric, and thusforms a mechanical bond between the mesh structure and the fabric.Provided this is carried out properly and provided the correct meshstructures are used, melting the surfaces of the thicker parts does notweaken the mesh structure significantly.

However, other methods of laminating are possible, such as flame or hotmelt adhesives bonding, but it is preferred to avoid any shrinking oforiented strands or adherence of the fabric to strands--thus the flameor the hot melt adhesives are preferably not applied excessively or atall to the strands.

The mesh structures are preferably such as to have pronounced nodules ofunorientated or low-orientation plastics material in the junctions, andsuitable mesh structures can be made in accordance with U.S. Pat. No. 4374 798.

PREFERRED EMBODIMENTS

The invention will be further described, by way of example, withreference to the accompanying drawings, which:

FIG. 1 is vertical section through the paved surface of a road; and

FIG. 2 is schematic view showing the formation of a laminate inaccordance with the invention.

FIG. 1

FIG. 1 shows a road base 1 which forms the ground to which has beenadhered the fabric 2 of a mesh structure/fabric laminate 3 whichincludes the mesh structure 4. The fabric 2 is lowermost, and has beenadhered to the road base 1 in any suitable manner, as discussed above.Aggregate 5 has been placed on the laminate 3, and the pieces of theaggregate 5 pass into the meshes of the mesh structure 4, engages in themeshes, and interlock with the strands of the mesh structure 4. Theaggregate 5 has been subjected to pressure in order to consolidate it,forming a flat road surface 6. Though the strands of the mesh structure4 may be somewhat pressed down, it is found that some of them standslightly proud of the fabric 2 and interlock with the pieces of theaggregate 5.

FIG. 2

FIG. 2 shows a known laminating machine having a heated roll 11 whoselower half wrapped by a silicone rubber belt 12. A fabric 2 and aplastics material mesh structure 4 are fed between the roll 11 and belt12 so that the roll 11 heats the high points or nodules (i.e. thethicker parts) of the mesh structure 4 through the fabric 2 andlaminates them together to form the laminate 3.

By melting only the surface of nodules of the mesh structure 4 andpressing the fabric 2 onto the nodules, the molten plastics materialpenetrates the fabric 2 and produces a mechanical bond. Due to thearrangement, the heated roll 11 has little effect on the orientedstrands of the mesh structure 4.

EXAMPLE

The machine of FIG. 2 is used to make a laminate.

Mesh structure:

The mesh structure is in accordance with FIG. 21 of U.S. Pat. No.4,374,798. The mesh structure is a biaxially-oriented mesh structurehaving rectangular meshes, and formed by oriented strands connectedtogether at junctions. Each junction has a thick unoriented orlow-oriented zone or nodule in its centre, surrounded by thinner, moreoriented zones. The nodules are much thicker than the strands.

The mesh structure is made of polypropylene, which during manufacture isheat set and thus made resistant to reversion (shrinkage) at asphaltlaying temperatures.

    ______________________________________                                        Grid mesh pitch   70 mm × 50 mm                                         Grid unit weight  240 gms/m.sup.2                                             Grid thickness at nodules                                                                       4.4 mm                                                      Grid width        4.0 mtrs                                                    Fabric:                                                                       Raw material      polyester                                                   Fabric constructions                                                                            needled continuous filaments                                Fabric weight     130 gms/m.sup.2                                             Fabric width      4.0 m                                                       ______________________________________                                    

The laminate was used as described in relation to FIG. 1 to form a roadsurface using a conventional asphalt paviours to lay the asphalt. Theadhesive was spread on the ground before placing the laminate inposition after which further adhesive was applied on top of the fabric.The adhesive was a bituminous aqueous-based emulsion, sprayed on at arate of 11/2 to 2 liters/m² of ground; a lower rate, e.g. 0.8 to 1liters/m² can be sprayed on if push brooms are used to brush the fabricdown onto the adhesive surface or automated lay-down equipment used. Theasphalt was a rolled asphalt wearing course (Design Mix), laid asfollows:

    ______________________________________                                        Thickness of layer                                                                             50 mm                                                        Aggregate size   20 mm maximum (graded)                                       Laying temperature                                                                             140°-150° C.                                   ______________________________________                                    

The present invention has been described above purely by way of example,and modifications can be made within the spirit of the invention.

We claim:
 1. A method of providing a paved surface,comprising:positioning a mesh structure/fabric laminate on the groundwith the fabric lowermost, and adhering the laminate to the ground; andplacing aggregate on the laminate to form said paved surface, wherebyaggregate engages in meshes of the mesh structure and the surface isreinforced by said laminate.
 2. The method of claim 1, wherein thelaminate is adhered to the ground by applying adhesive to the ground andlaying the laminate on the ground, and by then applying further adhesiveto the upper face of the fabric of the laminate prior to placingaggregate on the laminate.
 3. The method of claim 1, wherein thelaminate is adhered to the ground using a bituminous liquid.
 4. Themethod of claim 1, wherein the mesh structure comprises strands andzones which are thicker than the strands, which zones are secured to thefabric to form the laminate.
 5. The method of claim 1, wherein said meshstructure is a plastics material mesh structure comprising orientedstrands connected to each other at junctions containing zones which aresubstantially thicker than the strands, stand proud of the strands andcontain plastics material which is unoriented or of low orientation, andsaid fabric comprises fibers or filaments, said fabric being engaged bysaid thicker zones with said thicker zones enveloping some said fibersor filaments to thereby bond said thicker zones to said fabric, saidstrands not being substantially bonded to said fabric.
 6. A method ofproviding a paved surface, comprising:providing a mesh structure/fabriclaminate, the mesh structure comprising strands and zones which arethicker than the strands, the mesh structure defining open meshes, thefabric being secured only to said thicker zones to form said laminate;positioning the mesh structure/fabric laminate on the ground with thefabric lowermost, and adhering the laminate to the ground; and placingaggregate on the laminate to form said paved surface, whereby aggregateengages in meshes of the mesh structure and the surface is reinforced bysaid laminate.
 7. The method of claim 6, wherein the laminate is adheredto the ground by applying adhesive to the ground and laying the laminateon the ground, and by then applying further adhesive to the upper faceof the fabric of the laminate prior to placing aggregate on thelaminate.
 8. The method of claim 6, wherein the laminate is adhered tothe ground using a bituminous liquid.
 9. The method of claim 8, whereinsaid zones are comprised in junctions interconnecting said strands. 10.The method of claim 6, wherein said mesh structure is a plasticsmaterial mesh structure comprising oriented strands connected to eachother at junctions containing zones which are substantially thicker thanthe strands, stand proud of the strands and contain plastics materialwhich is unoriented or of low orientation, and said fabric comprisesfibers or filaments, said fabric being engaged by said thicker zones ofsaid mesh structure with said thicker zones enveloping some said fibersor filaments to thereby bond said thicker zones to said fabric, saidstrands not being substantially bonded to said fabric.